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The vast majority of cars, trucks and buses on our city streets still run on fossil fuels. Hybrid and electric cars are undoubtedly on the rise, and biofuels and fuel cells are beginning to make their mark, but for now at least, high carbon emissions from transport remain a problem for all cities.

In a very real way, life depends on carbon dioxide (CO2). Through the process of photosynthesis, trees and plants use it to make food for themselves and oxygen for us to breathe. And its warming effect helps to protect us from extremes of temperature. For 3.2 billion years, this natural carbon cycle has regulated the movement and exchange of CO2 through our atmosphere, soils and oceans. Humanity tipped the balance when we started to pump more carbon into the atmosphere than our biosphere could absorb, altering our climate in the process.

Emissions from cars are an issue in cities the world over (Image credit: Prashanth Vishwanathan/Bloomberg)

But researchers from the University of Southern California have found a way to convert CO2 from the air into methanol (CH3OH) – a long-proposed fuel of the future. Led by G. K. Surya Prakash and Nobel Laureate Prof George A. Olah, this work involved bubbling air through a solution called pentaethylenehexamine (essentially, lots of nitrogen, carbon and hydrogen bonded together). The CO2 latches onto the available hydrogens and when heated, you’re left with methanol and water.

Producing methanol from carbon dioxide and hydrogen isn’t new, but the key to this ‘one pot’ process, published in the Journal of the American Chemical Society, was its ruthenium catalyst. It allowed the reaction to happen at much lower temperatures than previously achieved, and could convert up to 79% of the captured CO2 into methanol. Industrialisation of this process is still 5 – 10 years away, but plans are afoot.

The Californian team aren’t the only ones exploring this area either. In the heart of Canada’s oil region, a small company called Carbon Engineering (CE) is developing an industrial process that literally sucks carbon dioxide from the air. At the front of its system, a huge wall of fans pulls the air in, where it’s passed through corrugated sheets of plastic coated with potassium hydroxide. Several chemical steps later, it produces pure CO2 in gas form, which can then be used to manufacture ultra-low emission fuels. CE has great ambitions for this technology, and aim to build a plant that could capture 1,000,000 tons of carbon dioxide a year – equivalent to that produced by around 213,000 cars (based on EPA figures for an average passenger vehicle). This is particularly relevant when we consider that, according to Prof David Keith, President of CE, “small, mobile sources like cars, trucks and planes… together make up 60% of today’s total carbon emissions.”

Carbon capture is one part of a bigger solution that includes renewable energy technologies (Photo by Spencer Platt/Getty Images)

There is no doubt that efforts like this are impressive, and a novel way of looking at the issue of an excess of CO2 in the atmosphere. But there are plenty who worry that this will be used to justify the continued burning of fossil fuels, bringing a kind of “Oh but its ok to burn fuel, we have systems that will suck it back out of the atmosphere later” attitude to the situation. However, as one part of broader effort to stabilise (or reduce) carbon dioxide levels in the atmosphere, it’s worth considering.

Right now, the fuels produced from these systems are costly, but researchers in the area are positive about the future. "Of course it won't compete with oil today, at around $30 per barrel," Prof Prakash said. "But right now we burn fossilized sunshine. We will run out of oil and gas, but the sun will be there for another five billion years. So we need to be better at taking advantage of it as a resource."